Age-hardening and tensile properties of low gold (10-14 kt.) alloys.

The age-hardening and tensile properties were determined for seven 10-14 kt. gold alloys, a conventional type II, and a sterling silver alloy. For the low-gold alloys the heat hardening curves indicated that the maximum aging effects were attained after 30 min at 400 degrees C. From tensile tests on either wire or dumbbell specimen configurations, Young's modulus (E), proportional limit (P.L.), ultimate tensile strength (U.T.S.), and elongation to break were measured for alloys in both the solution annealed (S) and the hardened (H) state. These stress-strain data not only confirmed previous correlations noted for conventional gold alloys between either E, P.L., or U.T.S. and hardness and between U.T.S. and P.L., but also varied systematically with the Au/Cu ratios in the (H) state. Under identical heat treatment and tensile testing conditions, comparison of the manufacturers' cast samples with this laboratory's specimens showed that, while the E, P.L., and U.T.S. differed somewhat, the greatest change occurred in the elongation to break. Here after measuring the porosity of the different specimen configurations and analyzing the log10 elongation with VHN, the conclusion was clear: Specimen geometry markedly influenced the physical properties. On this basis the proposed dumbbell geometry is advocated over the wire specimen configuration currently cited in ADA Specification No. 5.